It is implied it is fast as flavor, which is the whole point.
One turn gives a single full-round action. Which is worth one standard action and one move action. And a standard action is worth two move actions. Move < Standard < Full Round, as defined by your PHB.
Now what is a swift action worth?
1. You get one full-round action per turn, and one swift action, it must be worth a full round as far as time goes.
2. 1 can't be right since happens along side a full-round action, hmm. Maybe its so small we can't note it?
3. If 2 is true then why can't I give up a move action for multiple swift actions or something?
4. Why keep going and not admit that swift actions don't even fall into the full round/standard/move action setup and is the 'new' official keyword to the free action but only on your turn stuff that was limited to once per round for balance reasons and given flavor (thats flavor, not rules) that it happens in a really 'small' amount of time?
Since there is not way to explain swift actions in game and 75% of all flavor don't even match the rules. The flavor comment its is a 'small' amount of time can go to the same place that rogue using UMD to spend turn uses went. Which leaves us with the rules and the fact its not even part of a full-round action. <inset another apple & orange or Lucus bash here>
@Rebel7284, the Fire Blooded template (some dragon magazine) grants daze immunity.